A transmit/receive switch is commonly used within a frontend of an ultrasound system to switch between a transmit phase and a receive phase of an ultrasound scan. The transmit/receive switch allows the transducer elements of the ultrasound system to be used for both the transmit phase and the receive phase. The switch may provide protection for the receiver electronics from the high voltage signals used during the transmit phase.
In transmit/receive switch arrangements, an electrical load at the transducer elements during the receive phase is mainly provided by the resistance of the closed switch and the input impedance of a subsequent low noise amplifier. An impedance ratio between the transducer elements and the combination of the closed switch and low noise amplifier influences the performance of the ultrasound system. For example, reverberation artifacts may be minimized by matching the impedance of the transducer with the impedance of the combination of the closed switch and low noise amplifier. The minimization of the reverberation artifacts can be important, for example, at a depth of a few centimeters during an ultrasound examination of a pregnant uterus, i.e., at the amniotic fluid.
Existing transmit/receive switch and low noise amplifier arrangements that provide control of a switch resistance may not be desirable because the gain of the low noise amplifier varies with the adjustment of the switch resistance. Further, existing transmit/receive switch arrangements that adjust a switch resistance to match the impedance at the transducer may not adequately reduce the input signal level into the low noise amplifier in the near field, when the receive voltage level is high, to overcome saturation effects of the low noise amplifier. Existing transmit/receive switch arrangements that adjust a switch resistance to match the impedance at the transducer may also not consider the noise floor in the far field. For example, the switch resistance control of existing systems can be inadequate for setting the impedance of the transmit/receive switch to a low value to minimize the noise floor.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.